1. Field of the Invention
The present invention relates to screwdrivers. More particularly, the present invention relates to a screwdriver comprising a slider having an attached screw bit and a position detector for position feedback.
2. Description of the Prior Art
Automated screwdriver systems have been employed in mass production of various devices, such as a disk drive comprising a head stack assembly (HSA) that is fastened to a base, and a cover fastened to the base. The screw driving process typically comprises a “search step” wherein the screw is moved toward the work surface while turning at a low rotations per minute (RPM). When the threads of the screw begin to engage the work surface, the torque of the screwdriver will typically increase beyond an engagement torque threshold. Once the threads have engaged the work surface, as indicated by the torque exceeding the engagement torque threshold, the screw is rotated at a high RPM during an “angle step” to expedite the screw driving process. After a predetermined number of revolutions (angular driving degrees), the screw is rotated at a medium RPM to apply a final torque to the screw during a “torque step.” The screw driving process is considered complete when the torque exceeds a final torque threshold.
A number of problems have been identified with the above-described prior art screwdrivers. First, for small screws the engagement torque may be too small to detect, and therefore the screwdriver may never transition into the high RPM angle step. That is, the screw may be screwed completely into the work surface using the low RPM of the search step, which can significantly increase the screw driving time, and/or the screw driving process may fail altogether. Another problem is that at the end of the screw driving process, the prior art screwdrivers may not be capable of accurately verifying the final position of the screw relative to the work surface. Thus, for example, if the torque applied by the screwdriver exceeds the final torque threshold due to cross-threading, the prior art screwdrivers may not be capable of detecting this error condition.
There is, therefore, a need for a screwdriver capable of detecting when the screw has contacted the work surface in order to transition into a high RPM angle step. There is also a need for a screwdriver capable of verifying the final position of the screw relative to the work surface.